if you do a low poly and low res game you could maybe render a couple of viewports on a 4090, but for full scale say 1080p this is not gonna work. you would have to dedicate multiple gpus to 1 client to even get close to 30 fps realtime performance and that’s a hypothetical assumption.
i myself need 3 seconds a frame in blender cycles on a 3060 (theoretical 1/7th of a 4090). and that is a simple scene and quite optmized render setup, with lowest amount of bounces and samples required. basicly everything that produces noise gotta be lit analytical. so… basicly barely gi and partially faked for the render performance. i dunno the numbers on ue5’s pathtracer. i have not benched it, yet. i’d have to port a scene to get a comparison.
with megalights™ you have the opportunity to fake most of the gi and can have stable performance, so this fake/artistic route is more compelling, than going full on path tracing. lumen will assist and make the reflections look good aka very much usable. this could maybe work in this pixel streaming scenario.